Looping background (png image) in Blender for a car chase scene
That's not too hard actually:

I just move the UV coordinates around.


Create a seamless background image. Left and right borders should match.
UV-Map it on a plane that fills your background.
Use the Node Editor for the material and create this node setup:




The texture coordinates are provided to a Vector Math node. There, I am adding both vectors together, animating the yellow, formerly static one. Just click the button, set the X value, exist and set a key frame. It simply creates an offset for your UV coordinates, shifting the image around the plane.



As many frames as you want later, crank the value up and set another key frame. With the node selected, go into the Graph Editor and set the interpolation to linear in order to get a nice and smooth motion.



I deleted the other two channels since the motion is only in one axis.

Only drawback is that motion blur won't work with Cycles. You could blur the texture though.